The invention relates to a fuel cell with a solid oxide (SOFC)--or a molten carbonate salt electrolyte (MCFC), (SOFC=solid oxide fuel cell; MCFC=molten carbonate fuel cell). It further refers to a process for the production of an anode for the fuel cell.
Fuel cells are the subject of study because of their high energy conversion efficiency. They operate by converting chemical energy of fuels directly to electrical energy without the need for a thermal energy conversion step. This efficiency (not subject to the Carnot cycle limitations) coupled with (i) advantageous operating characteristics even at partial load, (ii) the possibility of co-generation of energy and (iii) production of low pollutants, makes the fuel cell a potentially important energy conversion device.
The present invention relates more specifically to a fuel cell of the type which is a ceramic fuel cell. As is usual with fuel cells, the device produces electricity by electrochemically combining fuel and oxidant gases across a separator. Ceramic fuel cells use an ionic conducting oxide and usually use an oxygen-ion conductor or a proton conductor as the electrolyte. The ceramic construction allows operation at high temperatures (greater than 600.degree. C.).
A high-temperature fuel cell with a solid [oxide] electrolyte (SOFC) requires high reliability of all operating parts over an adequate time span during operation. In order to achieve this, at the present time systems of different sizes are being tested worldwide. In general, so-called classical materials are used with various modifications.
These materials include:
Zirconium oxide fully stabilized with yttrium (8 mol. %) (YSZ) as the electrolyte; PA1 Perovskite (LaMnO.sub.3) doped with strontium for lanthanum, and with cobalt for manganum, as the air electrode (cathode), PA1 CERMET of a mixture of metallic nickel and YSZ, as the fuel electrode (anode), PA1 A metal (Cr-base alloy) or ceramic (doped perovskite of lanthanum chromite) plate as an interconnector (bipole plate) to connect together cells into a stack.
One of the serious problems of this system lies in the fuel cell anode. Due to the thermodynamic instability of the interface between metal and ceramic, the nickel metal of the anode tends toward restructuring with a resultant loss of electrochemical activity and a breakdown of the electrical conductivity of the electrode. This effect is particularly great in the case of contamination of nickel with impurities, such as, e.g., sulfur or sulfur compounds present in gaseous fuels obtained by the gasification of various carbon products.
In addition, the nickel metal exhibits too high a catalytic activity for the internal reforming of a methane-water vapor mixture, whereby the electrode can be poisoned by the deposition of carbon at the three-phase boundary. Proposals to reduce the high catalytic effect in reforming by a partial or complete replacement of Ni by Pd or Co are currently being tested. However, the problems of the instability of the interface in CERMET cannot be resolved with these systems.
It is therefore an object of the invention to provide a fuel cell, including an anode, which avoids the problems of the art.